Dirac cones at k→= in acoustic crystals and zero refractive index acoustic materials

Abstract

We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at k→=0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/κeff and zero mass density ρeff, and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials.